The patented BSSI Self-Pressurizing Overtemperature Capsule (SPOC™) is an integrated, automatic system for maintaining the fluid inventory in an antifreeze system. The SPOC™ maintains the fluid level, accommodates expansion and contraction during operation, vents air bubbles from the flow circuit, manages system pressurization, and protects system components and the antifreeze fluid from over-temperature damage if the collector system is stagnated.

How it Works:

The SPOC™ is mounted above the highest point of the collector system, with a small tube connecting it to the collector loop plumbing. The SPOC™ consists of a radiator section followed by a radiator cap and then a reservoir, as shown in the illustration above.

Since the SPOC™ is not directly in the collector flow path, it stays cool during normal system operation. As the system heats up and the collector fluid expands, the radiator cap regulates the pressure in the system to a maximum of 16 psi by venting a small amount of fluid into the reservoir. Any air bubbles that have risen to the top of the collector are driven out with this fluid and bubble out through the fluid in the reservoir. When the system cools again, pure antifreeze fluid (without bubbles) is drawn from the reservoir back into the system through the vacuum breaker valve in the radiator cap. A fluid level switch located in the reservoir is used to notify the system owner if the level becomes low and requires refilling.Over-temperature protection:
If the system stagnates for any reason, the collectors will begin to overheat. At 16psi pressure, the antifreeze solution will begin to boil when the temperature reaches 247°F (119°C). Steam exiting the collector enters the radiator section of the SPOC™, where heat transfer to the air condenses the steam flow. The condensed fluid then drains back to the collector. This process continues as long as the collector is stagnated, protecting the system from boiling dry or overheating beyond 247°F (119°C) and thereby preventing the breakdown of the propylene glycol into glycolic acid, which would corrode system components.

SPOC Features:

Simple installation

No user intervention required

Automatic control of collector fluid inventory

Automatic venting of air bubbles in the collector loop

Automatic pressure regulation of the collector loop

Automatic over-temperature protection for system components and for the collector fluid

Available in one stock size for residential solar hot water systems, and as SPOC-MEGA™ systems that are made to order for commercial systems

System pressurizes itself automatically upon first operation; no pre-pressurization is needed

Simpler Installation and Operation: Typical glycol systems use a pressurized expansion tank to accommodate the expansion and contraction of the antifreeze during system operation. These tanks are large, expensive, and cumbersome to install. The BSSI SPOC™ is easy to install at the top of the collector. Competing systems require manual pre-pressurization of the collector loop. Then, after the system has operated for several days, they require manual venting of air that was dissolved in the antifreeze. For installers, this means having a pressurization system, and the venting requires a second trip to the installation site, and another climb onto the roof to actuate the vent valve located at the top of the system. Venting may even need to be repeated as additional air comes out of solution over time. The BSSI SPOC™ performs both the pressurization and venting of the system automatically and continuously.

No Metal Pipes Needed: Typical competing systems operate at much higher pressures, requiring metal pipe or tube for the collector loop. The BSSI SPOC™ system limits the system pressure to 16 psi at the collectors, and system temperatures to 247°F (119°C), so high-temperature rubber hose can be used instead of metal tubing. This is less costly and makes installation of our system much easier.

Stagnation Protection: Some systems simply allow the pressure in the system to rise until the collector reaches a stable stagnation temperature without boiling. But those temperatures can reach hundreds of degrees Fahrenheit, leading to high pressures and conditions under which the glycol can thermally degrade. Still other systems steam formation in the collectors to push the liquid out, and then allow the collectors to stagnate with just steam inside of them. However, when liquid tries to re-enter the collector, it contacts the very hot surfaces of the dry collector, leading to thermal degradation of the glycol. The BSSI SPOC™ system, with its passive heat dump and pressure regulation, provides a thermal load during stagnation conditions that prevents the collectors and glycol fluid from reaching temperatures or pressures that could cause damage.

Installing a SPOC™ in a system with more collector area than the maximum stated in the table will void the warranty and can lead to boiling over. Boiling over can lead to the collectors and overflow reservoir running dry. Once this happens, the system will heat up well above the 247°F limit, and air can be drawn into the closed loop which will degrade the propylene glycol, potentially forming glycolic acid which will corrode your solar collectors. Butler Sun Solutions, Inc. will not be liable for damages caused by improper use of this product.

Typical SPOC-MEGA dimensions are given for comparison, but MEGA systems made to meet the requirements of specific commercial applications are no longer available.

This data is representative of this product’s performance, but acceptability for a specific solar collector size or collector system type should be verified by, and is the responsibility of, the user.